Measuring instrument



Jan 30, 1940- E. FREYs'rl-:DT

MEASURING INSTRUMENT Filed Nav. 26, 1937 ATTORNEY.

Patented Jan. 30, 1940 UNITED STATES PATENT or-'FICE MEASURING INSTRUMENT Application November 26, i987, serial No. 176,787 In Germany November 27, 1936 8 Claims.

This invention relates to measuring instruments and more particularly to means for measuring the volume of liquid in a container which is unsteady in space.

Devices heretofore proposed for measuring the volume of liquid in a container wherein the condenser method is employed have measured the capacity o1" a condenser disposed in the liquid in the form of a sounding device with said liquid acting as the dielectric, such measurement being taken by means of a measuring bridge in cooperation with a dry rectifier bridge fed by an alternating current generator. In this as well as in many other previous arrangements of this character, it has been necessary, in order to produce accurate indications, to use multi-stage thermionic tube amplifiers in addition to special batteries all of which involve a considerable increase in weight of the complete apparatus thus reducing the adaptability thereof for use in vehicles such as aircraft.

One of the objects of the present invention is to provide novel means, which are light in weight, for measuring the volume of liquid in a container which is unsteady in space.

Another object of the invention is to provide novel means for measuring the volume of liquid in a container wherein the condenser method is employed.

A further object is to provide novel means for measuring liquid volume in a container wherein the condenser method is employed and where it is unnecessary to employ therewith heavy electrical equipment.

An additional object is to provide novel condenser means for measuring liquid volume in a container wherein high sensitivity to volume change is obtained.

A further object is to provide novel condenser means for measuring liquid volume in a container wherein a measuring current is employed at a low voltage and a high frequency.

Another object is to provide novel means for liquid volume measurement wherein the volume of liquid in any pair of several tanks may be read from the same scale.

The above and further objects and novel features of the invention will more fully apear when the same is read in connection with the accompanying drawing. It is to be expressly understood', however, that the drawing is for purposes of illustration only and is not intendedto define the limits of the invention, reference being had primarily for this latter purpose to the appended claims.

(Cl. 'Z3-304) In the drawing:

Fig. l is a schematic representation of one em bodiment of the present invention, and

Fig. 2 is a schematic illustration of automatic means for balancing the bridge.

The form of the invention illustrated in the accompanying drawing, by way of example, is a measuring arrangement for determining the amount of liquid in a container regardless of the attitude of the container. Means are provided for measuring the capacity of a condenser disposed in the liquid wherein the condenser acts as a sounding device and the liquid serves as the dielectric medium. The measured capacity provides a gauge for the amountfof liquid in the container. Novel means are provided for causing an alternating current of low voltage and high frequency to flow to said sounding condensers and for comparing the capacity there obtained with a xed capacity. Variable-condenser means are provided for causing the twocapacities to agree by adding to or subtracting`from the capacity of the sounding condenser in such a manner that the amount so added or subtractedl is a measure of the volume of liquid in the container. l

One embodiment of the present invention is illustrated in the drawing. In order to better adapt the apparatus for installation, for example, aboard aircraft where limited space is available, it has been subdivided into a portion in housing 2 including a thermionic tube oscillator with measuring bridge and transformer means, a sounding condenser portion 3, and an indicating and control portion 4.

In order to avoid the use of heavy electrical equipment, such as multi-stage amplifiers and large transformers, which heretofore has been employed with apparatus of this character to produce a current of proper characteristics for ener-l gizing the sounding condensers, a high frequency low voltage thermionic tube oscillator 5 is pro- `vided comprising in the form shown a filament 6 indirectlyheated by element 1, a grid 8, and a plate 9. A suitable source of electric energy, as a battery 1a, is connected to element l with control resistance R, and coil Drin series therewith and with control condenser Ce in parallel. The apparatus does not require a separate energy source but may be connected, for example, to the vehicle battery. Tube 5 is in inductive return coupling to the grid circuit which coupling will be more fully described hereinafter. The high frequency low voltage output of thermionic tube 5 is fed to the sounding condenser bank 3 ,by

-windings W3 and W4 of transformer U1.

means of transformer U1 having windings W1 and W: with leads IIJ, Illa and II, IIa, respectively.

In the form shown, the capacity measuring bridge 3 is constituted by four sets of condensers I2, I3, Il, I5, which, for example, are adapted for sounding the four wing tanks of an aircraft. The condensers for each pair of tanks in the same-wing maybe in parallel and combined into a single sounding group, as group I2, I3 and I4, I5. parallel with leads I6 and I'I, in the second group with leads4 I8 and I9. Means are provided for energizing one of these groups at a time comprising switch r which is normally held in a position connecting contacts 20, 2| of the iirst group by means of a spring 20a. A relay 2Ia connected across battery Iathrough` a switch s at the control panel l is able to overcome the tension of spring 20a and to connect contacts 22, 23 to the energy source, thus energizing the second condenser group I4, l5.

For a purpose to more fully appear hereafter, there is connected across the transformer lead IIa and the sounding condenser output lead 24,V

the variable condenser Cs. In series therewith are variable capacities Cs and C10.

Inductively coupled by means of transformer Us to the sounding condenser circuit is the rectifier bridge circuit which acts in cooperation` with fixed capacities connected therewith to provide a reference capacity for `comparison to the measured capacity of thesounding condenser group. The rectifier bridge also serves to maintain indications of the greatest possible sensitivity and of accurate phase. Said bridge comprises rectiers 25, 26 which are respectively connected to one side of windings 21, 28 of transformer U2. Also'connected in the rectifier circuit are the windings serve to conduct symmetrically to the rectifier circuits an auxiliary voltage whereby the sum of the auxiliary and measuring voltages acts in one circuit and the difference in the other. To the opposite side of windings 21, 28 of transformer U2, in differential connection with rectifiers 25, 26, is the indicating instrument J. This connection is accomplished by connecting lead 29 to lead 30 which, in turn, is connected to J. Leads 3|, 32 are respectively connected to rectiers 25, 26 and also to instrument J. Between lead 30 and leads 3|, 32 there are connected the rectifying `capacitors C4 and C5 which act'in cooperation' with said rectifiers 25 and 26 to establish a fixed reference capacity and to enable a measurement by bridge means of the capacity of the sounding condensers.

It is seen that transformer U1 is in connection by means of lead 33, grid leak R2, and grid condenser Cz with grid 8, thus completing the inductive return coupling from plate 9 through transformer U1. Lead 28 connects transformer U2 to the negative side of battery 1a:

At the control panel 4 is attached the equalizing variable condenser Cs which is calibrated in .suitable units for liquid measurement upon a scale, the zero point and the maximum point of which are adjustable by means of the variable adjusting condensers C9 and C111. When these points are determined and it is desired Ato learn the volume of liquid in tank group I2, I3 the condenser capacity therein is balanced in the bridge circuits above mentioned against the rectifier capacity. ALack of agreement will cause a potential difference in the 'circuit which will cause a displacement of .the indicator J. Vari- The condensers of the first group are inv Said able condenser Ca may now be adjusted to restore the indicator to its original reading. The amount of adjustment necessary for Cs will be a measure of the volume and is readable upon the volume scale attached thereto. The use of an opposed bridge with the zero method, automatically compensates for temperature effects which might alter the readings.

Means are provided for compensating for the capacities of`1eads I6, I1, I8, I9, 34 and 35 which under ordinary circumstances would inuence the correct measurement of the capacity of the sounding condensers. Said leads are suitably screened or insulated vand the screens connected to housing 2 which serves as ground and by a ground connection to point 36 of the measuring bridge. Thus, the injurious screen capacities lie parallel to the bridge output and, therefore, are capable only of causing a reduced sensitivity of the indications at the control panel but not of causing rectifier errors.

In operation, the switch S is thrown to connect in the measuring circuit the desired group of sounding condensers, for example, group I2, I3. Thermionic tube 5 causes current at low voltage and high frequency to flow through the measuring bridge and sounding condensers by means of transformer U1. bank is coupled to the rectifier bridge by means of transformer U2. If the capacity existing in the condenser bank or sounding capacitors does not agree with the capacity of the rectifier circuit, a potential difference will exist and will cause the indicating instrument J to be displaced from zero. The equalizing condenser C must now be adjusted to bring the capacities of said two circuits into agreement. Said equalizing condenser is provided with a volumetric scale, the upper and lower limits of which, for an empty and a full tank, respectively, are determined by variable condensers C9 and C10. When the adjustment and capacity agreement is accomplished, the indicating instrument will be restored to the zero reading and the volume scale at the condenser Ca will register the amount of liquid in the tanks in question.

There is thus provided a novel volume measuring device which is capable of measuring the volume of liquid in a container which is not steady in space. The device is light in weight and avoids the use of heavy supplementary equipment. 'Ihe indications are extremely sensitive and easy to determine and the apparatus is adapted for indicating upon the same scale the separate volumes in several containers. The apparatus although employing the condenser method for determining volumes eliminates the necessity for multi-stage amplifiers and heavy transformers by employing an oscillator which produces a current of high frequency and low voltage. The device is further well adapted for installation within a limited space.

Although but one embodiment of the invention has been illustrated and described in detail. it is to be expressly understood that the same is not limited thereto. For example, in the form shown. a manual adjustment of condenser C8 is provided, however, automatic means such as The output of the condenser illustrated in Fig. 2 may be provided for adjustuntil indicator J is brought back to zero, apparatus is provided whereby automatic control of Ca is provided. A contact a is carried by the 'Ill pointer of instrument J andis mounted for movementy over contacts b and c. Whenever contact a is moved from its zero position into contact with either contact b or c a circuit is closed to motor e and source d whereby motor e by means of reduction gear f rotates the movable element of condenser Ca until the bridge is balanced and the pointer of instrument-YJ carrying the contact a returns to zero position. Various changes may also be made in the design and 'arrangement of parts illustrated without departing from the spirit and scope of the invention, as will now be understood by those skilled in the art. For a deiinition of the limits of the invention', reference will be had primarily to the appended claims.

What is claimed is:

1. In apparatus of the class described, means for causing a current to ilow at a high frequency, capacitor sounding means, a xedv capacity, means for causing said current to act upon said capacitor sounding means, means for comparing the capacity of said sounding means with the ilxed capacity, and means for bringing said capacities into agreement.

2. In apparatus of the class described, a container, an oscillator, a capacity measuring bridge in said container, a rectiiier capacity bridge, current indicating means for said rectiiier bridge, means for coupling said bridges, and means for determining the difference in the capacities of said bridges and for determining the volume of liquid in said container in accordance with said difference.

3. In apparatus of the class described, a container, condenser measuring bridge means in said container, means for energizing said condensers, rectiiler bridge means coupled to said measuring bridge, indicating means in differential connection with said rectifier bridge and said condenser measuring bridge, and means for causing said indicating means to be displaced in accordance with the capacity in said condenser measuring bridge.

4. In apparatus of the class described, a capacity measuring bridge, a rectier capacity bridge coupled thereto, a container of liquid, said iirstnamed bridge being disposed in said container,

means for comparing the capacities of said bridges, indicating means for determining the volume of liquid in said container in accordance with said comparison, and capacity means for determining the extremities of said indicating v means.

5. In apparatus ofthe class described, a plurality of liquid containers, condenser means in said containers, a predetermined balancing capacity, means for causing the' capacities of condensers disposed in said containers to be balanced with said predetermined capacity, and means for determining the volume of liquid in said containers in accordance with the magnitude of said balancing capacity.

. 6. In apparatus of the class described, a container, capacitor means disposed in said con,- tainer, a rectier bridge, means for coupling said bridge and capacitor means, thermionic tube means for energizing said capacitor means and bridge, means for symmetrically feeding an auxiliary current to said rectiiier bridge, means for measuring the capacity of said capacitor means, and means for balancing the same against the rectifier bridge capacity and for determining the volume of liquid in said container in accordance therewith.

7. In apparatus of the class described, means for causing a current to flow, a container for liquid, capacitor sounding means in said container, a fixed capacity, means for permitting said current to act upon said capacitor sounding means, means for comparing the capacity of said sounding means with said fixed capacity, means for bringing said capacitiesinto agreement and for measuring the volume of said liquid in accordance with the capacity necessary to cause agreement.

8. In apparatus of the class described, a container, a volume of liquidin said container, a capacitor in said container, a. fixed capacitor, means for measuring the capacity of said iirstnamed capacitor and comparingthe same to said fixed capacitor, and means for determining said volume in accordance with the diierence between said capacities.

p ERICH 

